1. Field of the Invention
The invention relates to alternating-current power generators working from batteries.
2. Description of the Related Art
Auxiliary power systems based on batteries provide backup electrical current when normal power is interrupted or unavailable. In his article, Marshall Brain broadly describes, “How Emergency Power Systems Work,” HowStuffWorks, Inc. 1998. As described, batteries are the power source in one of the main types of backup power supplies. Batteries are charged with and produce direct current. In contrast, most public electrical utilities provide alternating current due to limitations of direct current. In addition, most appliances utilize alternating current.
To make the power from batteries usable by household appliances, inverters are used to convert direct current to alternating current. However, inverters are relatively expensive because they require semiconductors such as Insulated Gate Bipolar Transistors (IGBTs). Inverters utilizing semiconductors cannot be used with reactive loads because the reactive load will quickly burnout the semiconductor component. Furthermore, the semiconductors generally have a limited lifespan. The short lifespan, coupled with the expense, makes inverters impractical for extended use.
Like batteries, the power from alternators cannot be used to directly power household appliances. Alternators connected to an internal combustion engine produce pulsating direct current. Such direct current is suitable for charging a battery. However, pulsating direct current cannot be used to power appliances that are configured to run on alternating current.
Generators connected to internal combustion engines are not practical for producing alternating current for household appliances. Generators connected to internal combustion engines rely on fuel. In many applications where electrical utilities are unavailable, so is the fuel needed to power internal combustion engines. Furthermore, voltages output by the generator depend on the rpm of the motor. In addition, the efficiency of such generators is limited by the electromotive effect.
In U.S. Pat. No. 1,691,986 issued to Nyquist, an apparatus and a method for generating pure sine waves of electromotive force are disclosed. Nyquist teaches to connect a battery producing a single voltage to two “distributors”, which are formed by a resistor system. The resistor system is formed by two potentiometer resistors, a respective one connected to each terminal of the battery. Then multiple taps, which are each resistors, connect at various points along the potentiometer resistor to a respective segment of a stator and commutator (i.e. “tributor ring”). A rotor can then be turned within the stator and commutator to produce an alternating sine wave. As shown in FIG. 2 of Nyquist, the resulting waveform has an uneven step-up; i.e. the height of each step near the baseline is shorter than a step near the apex of the wave. In addition, because the system utilizes resistors, the output voltage of the sine wave depends on the resistance of the load and the resistance of the circuit. As a result, the output voltage is variable.